Growth of world energy demand has prompted widespread research and development to identify alternative energy sources for satisfying such demand. One such promising alternative energy source is biofuel, which encompasses various types of combustible fuels that are derived from organic biomass. There is a strong desire to develop biofuels that are not only cost-competitive with fossil fuels but also offer environmental benefits and are renewable. One particular type of biofuel is biomass-derived pyrolysis oil. Biomass-derived pyrolysis oil can be burned directly as fuel for certain boiler and furnace applications. Biomass-derived pyrolysis oil can also serve as a potential feedstock in catalytic processes for the production of fuel in petroleum refineries. Biomass-derived pyrolysis oil has the potential to replace up to 60% of transportation fuels, thereby reducing the dependency on conventional fossil fuel and reducing its environmental impact.
Biomass-derived pyrolysis oil is produced through pyrolysis, including through recently-developed fast pyrolysis processes. Fast pyrolysis is a process during which organic biomass, such as wood waste, agricultural waste, etc., are rapidly heated to about 450° C. to about 600° C. in the absence of air using a pyrolysis reactor. Under these conditions, a pyrolysis vapor stream including organic vapors, water vapor, and pyrolysis gases is produced, along with char (which includes ash and combustible hydrocarbon solids). A portion of the pyrolysis vapor stream is condensed in a condensing system to produce a biomass-derived pyrolysis oil stream. Biomass-derived pyrolysis oil is a complex, highly oxygenated organic liquid that typically contains about 20-30% by weight water with high acidity (TAN>150).
The biomass-derived pyrolysis oil stream often has a high content of heteroatoms, such as sulfur, nitrogen, and oxygen, the removal of which can upgrade the fuel value of the biomass-derived pyrolysis oil stream. Oxygen is often present in the biomass-derived pyrolysis oil stream in the form of aromatic oxygenates. The oxygen can be removed from the biomass-derived pyrolysis oil stream through hydrodeoxygenation with hydrogen in the presence of a hydrodeoxygenation catalyst to form a hydrodeoxygenated pyrolysis oil stream. Hydrodeoxygenation cleaves the oxygen bond to the aromatic ring of the aromatic oxygenates. However, during hydrodeoxygenation, the aromatic ring of the aromatic oxygenates are converted to a naphthene intermediate, i.e., a cyclic paraffin, to allow for cleavage of the oxygen bond to the aromatic ring. The naphthene intermediate generally remains in the hydrodeoxygenated pyrolysis oil stream after hydrodeoxygenation. Unfortunately, the naphthene intermediate has low octane quality and degrades the fuel value of the hydrodeoxygenated pyrolysis oil stream.
Accordingly, it is desirable to provide methods and apparatuses for preparing upgraded pyrolysis oil that enable oxygen and other heteroatoms to be removed from a biomass-derived pyrolysis oil stream while minimizing degradation in fuel value that results from conventional hydrodeoxygenation techniques. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.